Airbags for automotive vehicles have been mandated by the National Highway Transportation Safety Administration (NHTSA) for many years since they protect passengers in vehicles during the impact phase of an accident. Typically, prior airbag systems comprise an airbag interfaced to a source of airbag propellant which inflates the airbag when a sensor in the system senses a vehicle impact above a certain velocity. The propellant, such as sodium azide, is usually in solid form in a canister. The sodium azide canisters are triggered by a pyrotechnic-type device which ignites the propellant. The burning propellant generates a high pressure gas which is used to inflate the airbag.
Although propellants and compressed gases are the common sources of energy for inflating automobile airbags and other airbag systems, they are potentially hazardous. Not only can they be dangerous in cases of accidental fire, but may prove to be attractive nuisances when juvenile delinquents learn how to use the energetic materials and components to construct weapons.
Another difficulty that arises with the use of propellants and compressed gases to inflate airbags is the effect of overpressure built up in the confined volume of air in the passenger compartment of the vehicle when the airbag inflates. When the bags are inflated with the external compressed gases they displace some of the compartment's air, thereby compressing the air outside the bags. In automobiles, the overpressure becomes dangerous if more than two bags are inflated simultaneously. Overpressure buildup may rupture the eardrums of passengers in the vehicles and cause other injuries. Thus, more extensive application of airbags for rear seats and side panel protection of passengers is not possible in conventional systems using external gases to inflate the airbags.
Inflatable airbags have the advantage of compact stowage before they are called upon to provide protection, and can be deflated rapidly in order to limit the time that they interfere with the driver's vision. Pre-formed cushion materials, such as foam padding, which also protect passengers, have the advantage that their cushioning properties can be tailored to maximize their practical potential in each application. However, they are commonly employed as fixed panels or bolsters or barriers. It would be desirable to combine the advantages of airbags with the advantages of rapidly deployed pre-formed cushions to accomplish complete protection of individuals in vehicles during accidents. Such results have not heretofore been achieved in the art.